3. Beamline instrumentation

This section provides a brief overview of the instrumentation available for various kinds of routine and in situ experiments.

If you have questions about any of these tools or wish to pursue other experimental options, contact the beamline staff.

3.1. Fluorescence detectors

The standard fluorescence detector at BMM is a four element silicon drift detector with an Xspress3 readout. This normally sits on a linear stage so that distance to the sample can be user-controlled and incorporated into beamline automation (Section 8).

We also have a single element silicon drift detector which is useful in certain situations. If your experimental setup requires placing the detector in an unusual orientation, the single element detector can be used. Unlike the 4-element detector, the single element is not required to remain in an upright orientation during operation. While the single element detector sees fewer photons, this versatility of setup is occasionally very helpful.

Fig. 3.1 (Left) Four element silicon drift detector. (Right) One element silicon drift detector.

Note

Thanks to funding from the CHIPS Act, BMM is the process of procuring a new 7-element SDD! Look for that in late 2024 or early 2025.

3.2. Area detector

An older model of the Pilatus 100K is available.

Fig. 3.2 Dectris Pilatus 100K

Please note:

• BMM offers only limited integration of data output into the beamline workflow.

• BMM has limited options for mounting and integrating the Pilatus into your experiments.

• This Pilatus has a rather small detection area and a rather large pixel size (about 170 microns).

BMM does not have access to a larger/better/faster detector and has no plans of getting a new area detector in the near future.

3.3. Sample wheel

At BMM, the standard ex situ sample stage is a laser-cut plastic disk. The disk has 24 or 48 slots cut from the disk. These are the sample positions.

This disk is mounted on a rotation stage. The slots are 15 degrees apart, so moving from sample to sample only involves moving through a known rotation angle.

The rotation stage is mounted on the XY stage, allowing alignment of the sample holder to the incident beam.

Fig. 3.3 The standard ex situ sample holder is a plastic disk with slots for the sample positions.

Here are photos of some of the sample holder options. There are designs which use slots or circles for the sample position. The circular holes are 13 mm, which is a common size for a pellet press. 13 mm pellets can usually slip snugly into those holes.

Samples can be packed into the slots or holes. More commonly, samples are prepared in some manner and affixed to the front of the sample holder with tape.

There is also a design which is, essentially, a normal disk cut in half. That one holds fewer samples, but is easier to load and unload from a glove box during sample preparation.

Fig. 3.4 (Left) A single-ring sample wheel with 24 sample positions. (Center) Double-ring sample wheels with 48 sample positions. For both styles, there are options with 13mm x 3 mm slots or 13mm diameter holes. (Right) A half wheel suitable for loading in a glove box.

3.4. Electrochemistry

At BMM, we have a BioLogic VSP-300 Potentiostat which is available for all manner of electrochemistry experimentation. This is a 6 channel model, allowing you to prep samples during measurements or to run multiple electrochemistry experiments in parallel, moving those cells into and out of the beam.

Fig. 3.5 The BioLogic VSP-300 Potentiostat

We run the vendor-supplied control software on a Windows 10 instance running in a virtual container.

We do not, at this time, have full EPICS-level control of the potentiostat, limiting the level of automation and integration with the rest of the beamline.

Also, BMM does not provide electrochemical cells. The user is expected to bring their own cells.

3.5. Temperature control

BMM has two options for experiments as elevated or reduced temperature.

3.5.1. Linkam stage

The Linkam stage has LN2 flow for cooling a sample down to 77K and a resistive heater to go up to 600C. The volume inside can be pumped or exposed to flowing gas. The sample stage at the center is modified to have a 3mm diameter hole for transmission XAFS.

Fig. 3.6 (Left) The Linkham stage mounted for transmission on the sample stage. (Right) The 25 L dewar used for cooling the Linkam stage.

BMM has two dewars for use with the Linkam. The 2 L dewar has enough capacity for about 2 hours of measurement. The 25 L dewar runs for about 14 hours and is the standard choice. The advantage of the smaller dewar is that it is smaller and might be needed for complicated setups were space is at a premium.

3.5.2. Displex Cryostat

BMM also has a helium compression cryostat capable of reducing temperature at the sample to around 10K and with a resistive heater allowing a sample temperature range of 10K to about 400K.

This Displex model is designed for low-vibration applications. as a result, it is a bit slow to cool down, requiring about 2 hours to get to 10K from room temperature. Sample changes are a bit laborious due to the construction of the vacuum shroud.

Fig. 3.7 (Left) The Displex cryostat and it’s compressor. (Right) The LakeShore 331 controller, used to control temperature for the cryostat shown to the left.

3.6. Glancing angle and thin film stage

We use this glancing angle stage for high throughput studies of thin film and other flat samples. The apparatus shown below rests on a rotation stage for moving up to 8 samples into and out of the beam. The rotation stage sits on a tilt stage, allowing fine control of the incident angle. Each sample position is a spinner, which is used to suppress diffraction from the substrate. In most cases, sample translation and sample alignment is fully automated.

Fig. 3.8 The glancing angle stage with 8 sample positions.

While a standing wave experiment might be feasible at BMM, the much more typical application is a simple glancing angle measurement in which the point of the shallow angle is to spread the beam out over the full length of the sample. This significantly increases the number of atoms involved in the measurement.